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  1. 1. HEAVY METAL CONCENTRATION IN THE SEDIMENTS AND FLESH OF BOE DRUM (Pteroscion peli) AND GREATER AMBERJACK (Seriola dumerili) FROM THE KORLE LAGOON ESTUARY, ACCRA, GHANA Agbo, N.W., Aboagye, R .H. and Amisah, S. Department of Fisheries and Watershed Management, Faculty of Renewable Natural Resources, Kwame Nkrumah University of Science and Technology Kumasi, Ghana ABSTRACT: The Korle Lagoon in Accra, Ghana, has become one of the most polluted water bodies on earth. Different aquatic organisms often respond to external contamination in different ways, where the quantity and form of the element in water, sediment, or food will determine the degree of accumulation.. Heavy metal concentrations in sediment were below the National Oceanic and Atmospheric Administration (NOAA), (1995) Sediment Quality Guideline for Estuaries over the period and ranked in the order: Pb> Zn> Cu> Cd. The result of this research showed that heavy metals were continuously deposited and removed from sediments into the water column of the Korle lagoon estuary. Also the study indicated that the levels of metal in the flesh of Seriola dumerili and Pteroscion peli were low for, copper and zinc but higher for Lead and Cadmium as compared to the World Health Organization Standard (2005). Heavy metal concentrations in the flesh of S. Dumerili and P. peli in relation to size revealed that both sizes accumulated higher lead and cadmium concentrations and lower Zinc and Copper concentration. The present study showed that consumption of fish from the Korle Lagoon estuary should be prohibited and should be discouraged because of the high levels of Pb and Cd in the flesh of Seriola dumerili and Pteroscion peli in both small and large sizes. Key words: Concentration, Heavy metals, Sediments, Seriola dumerili, Pteroscion peli ,Korle lagoon Estuary, Cadmium (Cd), Zinc (Zn),Lead (Pb),Copper (Cu)
  2. 2. INTRODUCTION In recent times, the coast of Ghana is encountering serious environmental challenges (Karikari, 2007) and the Korle Lagoon in Accra, Ghana, has become one of the most polluted water bodies on earth. It is the principal outlet through which all major drainage channels in the city empty their wastes into the sea. Large amounts of untreated industrial waste emptied into surface drains has led to severe pollution in the lagoon and disrupted its natural ecology. The increased levels of industrial activity and consumption by the urban population lead to the generation of copious quantities of waste (Boadi and Kuitunen, 2002). Agbogbloshie, a suburb of Ghana’s capital, Accra, and just adjacent the lagoon is a known destination for legal and illegal electronic waste (e-waste) dumping from industrialized nations, often referred to as a "digital dumping ground". Millions of tons of e-waste are processed each year in the local recycling workshops. A study by Greenpeace (2008) revealed excessively high metal concentrations in the soils of the open burning grounds and in the sediments of the lagoon.. Anything that stirs up the water, such as dredging and upwelling, can resuspend sediments. Resuspension may mean that all animals in the water, and not just the bottom-dwelling organisms, will be directly exposed to toxic contaminants (Begum, et al., 2009. Fishes assimilate these heavy metals through ingestion of suspended particulates, food materials and sometimes by constant ion exchange process of dissolved metals across lipophilic membranes like the gills and adsorption of dissolved metals on tissue and membrane surfaces (Begum, et al., 2009). Bio magnification can result in fish at the top of food chain containing hundreds more heavy metals than it appears in the water or in any single fish they eat. Seriola dumerili and Pteroscion peli are important fish species in the Korle lagoon fishery and are in high demand by the inhabitants of Accra especially those around the Korle lagoon. Inhabitants often prefer large sizes of Seriola dumerili and small sizes of Pteroscion peli. Since these species are carnivores they could possibly accumulate heavy metals which could be detrimental to those who consume them. Based on the above reasons the objectives of this study were to assess the concentration of zinc, lead, copper and cadmium in the sediment and flesh of Pteroscion peli and Seriola dumerili and to examine variations in heavy metal concentration in the flesh of the Pteroscion peli and Seriola dumerili in relation to size. MATERIALS AND METHODS The Korle lagoon is a coastal wetland that joins the Gulf of Guinea at a point near Korle Gonno; a suburb of Accra (Grant, 2006). It serves as the major floodwater conduit for the Accra Metropolitan Assembly (Fig 3.1), the lagoon is estimated to drain a total catchment area of 400 km2 (Karikari et al, 1998). The major hydrological input includes the Odaw River, two huge drains that border the lagoon, and rainfall including runoff. A mixture of land uses characterizes the areas adjacent to the lagoon (Boadi and Kuitunen, 2002)
  3. 3. Fig 3.1 Korle lagoon and its environs (IMDC, 2011) Fish samples were obtained from fishers at the estuary of the Korle Lagoon estuary and transported on ice in an insulated chest (Plate 1,2). A total of 8 samples were obtained monthly for each species over the four months period. Samples from each species were categorized into two classes based on the sizes obtained for each; Pteroscion peli (Small ≤14cm and large ≥ 15cm) and Seriola dumerili (Small ≤24cm and large ≥25 cm) and were stored in a deep freezer prior to the heavy metal analysis. Plate 1 Pteroscion peli from the Korle lagoon Estuary
  4. 4. Plate 2 Seriola dumerili from the Korle lagoon Estuary Three sediment sampling sites were selected from site A, site B and site C as shown in Plate 1, 2, 3. The sediment sample was taken from each site and was divided into three to ensure accuracy in the result for each site sampled. This was done for the four months study period; October 2011 to January 2012. The Ekman grab was used in collecting the sediments samples. At site B and C the Ekman grab was mounted in a boat, after releasing the instrument to the bottom the boat owner dived to trip the over lapping spring loaded with scoop, the depth of both portion could be between 1 to 4 meters whilst at point C, samples were taken by walking into the water to points where the water reached the knee and with the Ekman grab sediments were collected. Samples were stored in plastic bottles and packaged in plastic bags and were kept in a cool, dry and ventilated room prior to heavy metal analysis. Sampling point (A) is the area that receives frequent sea water at both low tides and high tides with no rock deposited on both side. Plate 3 Sampling point (A)
  5. 5. Sampling point (B) is the area affected by the influx of both fresh water and sea water and rocks are deposited on the right side of the curved channel Plate 4 Sampling point (B) Sampling point (C) is the area that receives fresh water frequently than sea water and also joins B in a slightly curved channel with rocks deposited on both sides. Plate 5 Sampling point (C) The total length and body weight of the fish samples after defrosting were measured with a centimetre rule and weighed with an electric scale (Sartorius model, BP 6100) and labelled after identification. Small part (5grams) of the flesh from its side were removed and chopped with the aid of stainless steel dissection instruments, while wearing surgical gloves. After, flesh samples were then digested with a di- acid mixture, (nitric acid, and perchloric acid in a ratio of 9: 4). One gram of the chopped flesh samples was separately taken and placed in a 100ml volumetric flask. Ten millilitres of di acid mixture was added. The content was mixed by swirling in the volumetric flask. The flask was then placed on a hotplate in a fume hood and heated starting at 90oC and raised to 200oC. Heating continued until the production of a red NO2 fume ceases. The contents were further heated until the volume was reduced to 3-4ml and became colourless
  6. 6. without being dry. It was made to cool to room temperature. The volume was made up with distilled water and filtered with a Whatmann filter paper. The filtrate was then diluted to 50ml mark in a volumetric flask with double distilled water. It was then poured into small containers. The containers containing the digested samples were kept at 4˚c in a refrigerator prior to heavy metal analysis. Sediment samples were labelled (according to their location) on the field and air dried at room temperature on a plastic sheet. The dried materials were grounded to pass through a 63µm sieve and stored in plastic bottles. Digestion was done for the sediments as it was done for the fish flesh samples at the Faculty of Renewable Natural Resources. Heavy metal analysis was done at the Anglo Gold Ashanti Laboratory. The concentrations of copper, cadmium, lead, and zinc, were determined with the aid of flame Atomic Absorption Spectroscopy, (AAS) (SpectrAA 220 model).A blank solution of the di-acid and distilled water used which contained no analyte element was made and after, a series of calibrated solutions of the di acid and distilled water containing known amounts of analyte element (the standards) were also made. The blank and standards were atomized in turn, with their respective responds measured. Graph of both responses were plotted. The digested samples were then atomized and their response measured. The concentrations of heavy metal in the sample were known by the calibration and the absorbance obtained for the unknown. All samples were accompanied by blanks at a rate of one blank per 20 samples. Replicate analyses were conducted for all the samples to evaluate the precision of the analytical technique. The results were expressed as total concentration (μg/g wet weight (ww). RESULTS AND DISCUSSION Copper concentrations in sediments were consistently fluctuating over the period and ranged between 4.38 μg/g ww to 5.90 μg/g ww from November 2011 to January 2012. A mean concentration of 5.12 μg/g ww was recorded for the estuary over the four month period. Lead concentration increased drastically from a mean value of 2.80 μg/g ww in October to 39.20 μg/g ww in December 2011. A decrease in the concentration of lead was recorded for January 2012. Zinc ranged from 9.76 μg/g ww to 14.66 μg/g ww but this decrease was inconsistent as concentration declined from 12.44 μg/g ww in November 2011 to 9.76 μg/g ww in December 2011. Cadmium concentration fluctuated over the period with highest concentration of 2.50 μg/g ww recorded in December 2011.
  7. 7. Table 4.1. Copper (Cu), Lead (Pb), Zinc (Zn) and Cadmium (Cd) concentration (μg/g ww) in the sediment from the Korle lagoon Estuary. Month n Cu Pb Zn Cd October 9 4.41±0.08 2.80±0.08 12.21±0.05 2.33±0.07 November 9 4.38±0.03 2.86±0.04 12.44±0.03 2.26±0.02 December 9 5.80±0.02 39.20±0.07 9.46±0.30 2.50±0.10 January 9 5.90±0.03 38.36±0.04 14.66±0.04 2.23±0.01 Mean 5.12±0.04 20.80±0.05 12.19±0.10 2.33±0.05 NOAA (1995) ERL 34.00 46.70 150.00 1.20 ERM 270.00 218.00 410.00 9.60 National Oceanic and Atmospheric Authority (NOAA), Sediment Quality Guideline (SQG), Effect Range low (ERL), Effect Range Medium (ERM) Values are mean± SD, n= number of samples Mean concentration of copper in Pteroscion peli over the sampled period was 5.11 μg/g ww. Copper (Cu) levels increased between 2.83 μg/g ww in November 2011 to 7.65 μg/g ww January 2012. In October 2011 concentration declined from 3.02 μg/g ww to 2.02 μg/g ww in November 2011. A mean lead (Pb) concentration of 2.73 μg/g ww was recorded over the study period. An increase and decrease in concentration alternated over the sampling period. Cadmium (Cd) concentration consistently increased from 1.48 μg/g ww to 2.91 μg/g ww over the study period. Zinc (Zn) concentration increased from November 2011 to January 2011 with values ranging between 13.58 μg/g ww to 23.11 μg/g ww for both months respectively. Between October 2011 and November 2011 concentration dropped from 14.09 μg/g ww to 13.58 μg/g ww. A mean concentration of 16.41 μg/g ww was recorded over the study period.
  8. 8. Table 4.2. Heavy metal concentrations (μg/g ww) in the flesh of Pteroscion peli from the Korle lagoon estuary Month n Cu Pb Cd Zn October 8 3.02 ± 1.21 2.62±1.92 1.48± 0.26 14.09±2.80 November 8 2.83 ± 1.23 2.87 ±1.92 1.51±0.28 13.58±3.31 December 8 6.92±0.91 2.51±0.73 2.81±0.23 14.86±4.27 January 8 7.65±0.93 2.95±0.57 2.91±0.78 23.11±6.99 Mean 5.11±1.04 2.73±1.28 2.17±0.38 16.41±4.32 WHO (1983) 10 2.0 2.0 1000 WHO (2005) - 0.5 0.5 1000 World Health Organization (WHO) Values are mean± SD, n= number of samples Concentration trend observed in Seriola dumerili varied to that of Pteroscion peli. Copper (Cu) concentration increased from November 2011 to January 2012 from 3.36 μg/g ww to 6.14 μg/g ww. A mean concentration of 4.43 μg/g ww was recorded over the period. Lead (Pb) concentrations over the period fluctuated between 2.07 μg/g ww in December 2011 to 3.01 μg/g ww in November 2011. A decrease in concentration was observed from October 2011 to November 2011 and that of November 2011 to December 2011.A mean concentration of 2.54 μg/g ww was recorded over the period. Cadmium (Cd) level of 1.75 μg/g ww was recorded as the mean concentration over the sampling period. Cadmium levels in Seriola dumerili were inconsistent over the study period between 1.35 μg/g ww to 2.95 μg/g ww. Zinc (Zn) concentrations increased from November 2011 to January 2012 with its level increasing from 13.43 μg/g ww to 14.98 μg/g ww respectively
  9. 9. Table 4.3. Heavy metal concentrations (μg/g ww) in the flesh of Seriola dumerili from the Korle lagoon estuary Month n Cu Pb Cd Zn October 8 3.38 ± 0.76 2.90 ± 2.08 1.42 ± 0.31 13.45 ± 6.26 November 8 3.36 ± 0.32 3.01 ± 2.07 1.35 ± 0.29 13.43 ± 6.34 December 8 4.85±2.32 2.07±0.43 2.31±1.20 13.76±6.04 January 8 6.14±1.52 2.20±0.37 2.95±0.88 14.98±4.66 Mean 4.43 ± 1.23 2.54 ± 1.23 2.03 ± 0.67 13.90 ± 5.82 WHO (1983) 10 2.0 2.0 1000 WHO (2005) - 0.5 0.5 1000 World Health Organization (WHO) Values are mean± SD, n=number of samples In order to examine variations in heavy metal concentration in the flesh of the two fish species in relation to size, a plot of total accumulation versus size were carried out for the two fish species (Fig 4.1 and 4.2). Heavy metal concentration in relation to size of Pteroscion peli increased with increase in size for October 2011 and December 2011, even though for November 2011, zinc concentration in Small Pteroscion was higher than that of large size. In January 2012, copper and zinc concentrations increased in small Pteroscion peli than in large size Pteroscion peli. Lead concentration in December 2011 was relatively higher in the small fishes than in large samples (Fig 4.1 below).
  10. 10. Fig 4.1 Variations in Cu, Pb, Cd and Zn concentrations in the flesh of Pteroscion peli in relation to body size (Small ≤14cm , Large ≥ 15cm) Fig 4.2.Variations in Cu, Pb, Cd and Zn concentrations in the flesh of Seriola dumerili in relation to body size (Small ≤24cm, large ≥25 cm)
  11. 11. Heavy metal concentration in October 2012 and November 2012 increased with increase in size as large size Seriola dumerili recorded higher levels than smaller Seriola dumerili. On the other hand, small fish size fishes had higher concentration of copper and zinc for December 2011 and January 2012. Lead concentrations in December 2011 were high in large Seriola dumerili than in small sizes. Physicochemical parameters for the four months (October 2011 to January 2012) sampling period was relatively uniform as shown in Table 4.4. Temperature conditions in the lagoon ranged from 26.60°C to 29.10 °C over the period, a consistent increase in temperature from November 2011 to January 2012 was recorded. Dissolve oxygen levels in the estuary was fairly constant over the sampling period even though some portions of the estuary recorded very low oxygen levels. pH level over the sampling period was relatively neutral. A high conductivity of 3901 mg/l was recorded in January 2012. Salinity levels were low over the sampling months and were relatively similar for the sampling months. A Total Dissolve Solid value of 1991 μs/cm was recorded in December and was the highest over the study period. Table 4.4. The physicochemical parameters of the Korle Lagoon from October, 2011 – January, 2012 Parameter n October November December January Temperature (°C) 3 26.81±2.32 26.60±3.40 29.10±1.10 28.50±0.20 DO (mg/l) 3 6.10±1.50 6.00±0.41 5.98±0.01 6.00±1.30 TDS ( μs/cm) 3 1748±538.09 1553±638.0 1991±0.05 1901±1.42 Salinity (ppm) 3 15.05± 4.12 14.77± 5.80 16.01± 0.01 15.98± 1.02 Conductivity (mg/l) 3 3588±653.7 3381±273.74 3008±0.01 3901±1.02 pH 3 7.30±2.30 7.16±0.54 7.07±1.40 7.18±1.10 Total Dissolve Solids (TDS), Dissolved Oxygen (DO), Values are mean± SD, n=number of data recorded The relatively high levels of cadmium in the sediments compared to the Effect Range Low (ERL) could be due to the high concentrations of dissolved salts or organic matter which reduces its accumulation in sediments. Lead readily accumulates in sediments and this could be the reason for the high levels recorded over the period as compared to lead cadmium and zinc. The low copper levels could be due to the regular mixing of the water column due to its fluvial flow rate. Moreover, during high turbidity, greater levels of zinc associated with suspended sediments are deposited with flocculated particles where it can and where it can particularly accumulate in anaerobic sediments (Hunt et al, 1992). Salt concentrations could create increase competition
  12. 12. between cations and metals for binding site. This may cause metals to be driven off from sediments into the overlying water, and this may often occur at estuary due to river flow inputs and tides. Decreased redox potential under hypoxic conditions could change the composition of metal complexes as metals bind to oxygen to form oxides and this could release the heavy metal ions into the overlying water at the estuary. pH may increase competition between metals and hydrogen ions for binding site (Connell et al, 1984). The lower levels of copper in the flesh of both fishes could be due to the role of copper as an ingredient, normally in the prosthetic group, of oxidizing enzymes which are important in oxidation-reduction processes in fishes (Moolenaar, 1998). Low level of Zinc recorded could be due to the up take of zinc readily by the study fish species which may not reflect in the flesh tissue (Hunt et al, 1992). High level of lead concentration could be due to the uptake and accumulation of lead by fish from water and sediment and this may be influenced by various environmental factors. Lead uptake by fish could reach equilibrium only after a number of weeks of exposure. Typical symptoms of lead toxicity include spinal deformity and blackening of the caudal region was observed in the obtained fish samples. Cadmium bio accumulates in organisms with the main uptake routes being dissolved cadmium from the water column and cadmium associated with prey items. This could be the reason for the high levels in Seriola dumerili and Pteroscion peli (WHO, 1992).Large fishes for both species had a higher metal concentration in Pteroscion peli and Seriola dumerili, but thoroughly there were no variations in metal concentrations between the two size classes for both fish species and may be due to similarities in bioavailability of the heavy metals to the two fish species (Pteroscion peli and the Seriola dumerili.) from the Korle lagoon estuary, since both fish species are piscivorous (Ferreira et al., 2004). CONCLUSION AND RECOMMENDATION Heavy metal levels in fishes sampled were less than what was found in the sediment samples. Heavy metals in sediment were continuously adsorbed and desorbed from sediments into the overlying water column. The sediment quality in terms of the heavy metals was acceptable but could pose a serious risk to the aquatic life of the lagoon estuary in future if nothing is done to check metal accumulation in the Korle lagoon estuary sediment. The four metal concentrations in the flesh of the two fish species were lower for Zinc and Copper but saw a high concentration for Cadmium and Lead as compared to the World Health Organization Standard (2005) hence not safe for human consumption. From the study however, it was also depicted that Pteroscion peli and Seriola dumerili accumulate heavy metals in their flesh regardless of size. The heavy metal concentrations in estuary have to be monitored on a more regular basis for the effects of pollution on other fish communities Accumulation of heavy metals in fish flesh may be considered as an important warning signal for fish health and human consumption. The present study shows that consumption of fish from the Korle Lagoon estuary should be prohibited and should be discouraged.
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